The cohort included 1,139 cases of RA, with 40% of these positive for either rheumatoid factor (RF) or anti-CCP. Also, 467 cases were patients with systemic lupus erythematosus (SLE) and 180 cases were patients with other autoimmune diseases, such as systemic sclerosis. The investigators found that, in addition to the 10% increased risk of RA in individuals exposed to military dust compared with those who had minimal to no exposure to inorganic dust, other covariates included in the model were also statistically associated with an increased risk for RA. These covariates included age at first VA appointment, being female, a history of smoking and Hispanic ethnicity.
The investigators also documented that military dust exposure was associated with a 23% increased risk for systemic sclerosis, vasculitis or inflammatory myositis. In contrast, dust exposure was protective with regard to systemic lupus erythematosus. When the researchers analyzed the relationship between dust exposure and disease in women and compared that with the relationship in men, they found dust was statistically protective for eight years for women but was not statistically protective for men. The authors addressed this unexpected finding in their discussion, noting, “Only 12% of our cohort was female, and, moreover, work exposures even within JEM [job exposure matrix] categories likely differed systematically by sex. This complicates the interpretation of autoimmune diseases for which sex is a powerful risk factor and may account for the statistically significant protective effect of exposure for SLE among women [but not men].”
When the researchers disaggregated the patients according to serologic status, they found dust exposure was a statistically significant risk factor for seronegative RA, but not for seropositive RA. When they used models stratified by years of service, they found dust exposure in those with four to eight years of service was most strongly associated with a risk for RA and no statistical association among those with either fewer or more years of service.
An Occupational Laboratory
“Nobody has looked exactly this way at the risk of RA as a consequence of military operations writ large,” says principal investigator Paul D. Blanc, MD, MSPH, professor of medicine at the University of California, San Francisco.
Although he acknowledges the excess risk is modest, he points out that because it applies to many people, it’s noteworthy. “When you have a patient with a new diagnosis of rheumatologic disease, you should take an occupational history,” Dr. Blanc says. Such information may be useful in obtaining worker compensation from the military. He explains that although at the civilian level a 10% increased risk may not be justification for workers’ compensation, exposure to agent orange is associated with a similar magnitude of increased risk to multiple diseases and the military provides workers’ compensation for medical conditions associated with this exposure.2,3